The goal of the proposed project is to determine how muscle activation patterns of lower limb muscles adapt to compensate for the loss of one muscle's force output. Human subjects will perform an isometric plantar flexion task under normal conditions and then with either an involuntary (electrical stimulation induced fatigue) or voluntary (EMG biofeedback induced change) disruption of the lateral gastrocnemius muscles force output. Surface electromyographic recordings will be used to monitor and record muscle activity from several lower limb muscles during the exercise period. Magnetic resonance imaging will be performed immediately following exercises to reveal the spatial distribution of muscle activity in lower limb muscles. Together these techniques will yield an accurate temporal and spatial picture of muscle activity. If changes in Soleus activity occur, H-reflex testing will be used to start looking for where in the CNS the adaptation may be taking place. Overall the hypothesis of this study is that similar muscle activity adaptation can be elicited through both involuntary and voluntary methods of muscle force output loss. The results of this project will have benefits for rehabilitation of patients who have had muscle function loss due to disease or injury.